lkml.org 
[lkml]   [2002]   [May]   [5]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patches in this message
/
Date
From
Subject[patch] enable uptime display > 497 days on 32 bit (1/2)
The long promised next round of the 64 bit jiffies patch uses a new
lock-free scheme to update the higher word of the jiffies counter,
as suggested by Albert Cahalan:
Updates are now exclusively done by a long-running timer, thus needing
no locking. The reader just has to check whether the latest wraparound
is already accounted for, and adjust accordingly.
To keep this check simple, the high word of jiffies stores
bits 62-31 instead of 63-32, thus bit 31 is stored twice. If both copies
do not match, the high word needs to be incremented.
This technique indeed kept the patch simpler.

I've also added code to provide 64 bit (well, 63 bit) values of user,
nice, and system time in /proc/stat, as I've promised elsewhere.
However, I'm still not convinced this isn't creeping featurism.
It may be enough to just define these members of struct kernel_stat as
unsigned long, so that they don't overflow on alpha after 48.5 days.
Then again, these changes are fully local to the /proc fs, so they won't
blow up minimalistic setups without /proc.

As usual, a patch for debugging jiffies wraps follows.
A port to 2.5 and more testing will follow later.

Tim


--- linux-2.4.19-pre8/include/linux/sched.h Sun May 5 09:10:00 2002
+++ linux-2.4.19-pre8-j64/include/linux/sched.h Sun May 5 19:11:12 2002
@@ -363,7 +363,7 @@
unsigned long it_real_incr, it_prof_incr, it_virt_incr;
struct timer_list real_timer;
struct tms times;
- unsigned long start_time;
+ u64 start_time;
long per_cpu_utime[NR_CPUS], per_cpu_stime[NR_CPUS];
/* mm fault and swap info: this can arguably be seen as either mm-specific or thread-specific */
unsigned long min_flt, maj_flt, nswap, cmin_flt, cmaj_flt, cnswap;
@@ -579,6 +579,18 @@
#include <asm/current.h>

extern unsigned long volatile jiffies;
+#if BITS_PER_LONG < 48
+#define NEEDS_JIFFIES64
+ extern u64 get_jiffies64(void);
+#else
+ /* jiffies is wide enough to not wrap for 8716 years at HZ==1024 */
+ static inline u64 get_jiffies64(void)
+ {
+ return (u64)jiffies;
+ }
+#endif
+
+
extern unsigned long itimer_ticks;
extern unsigned long itimer_next;
extern struct timeval xtime;
--- linux-2.4.19-pre8/kernel/timer.c Sat May 4 19:32:34 2002
+++ linux-2.4.19-pre8-j64/kernel/timer.c Sun May 5 19:28:22 2002
@@ -66,6 +66,9 @@
extern int do_setitimer(int, struct itimerval *, struct itimerval *);

unsigned long volatile jiffies;
+#ifdef NEEDS_JIFFIES64
+static unsigned int volatile jiffies_msb_flips;
+#endif

unsigned int * prof_buffer;
unsigned long prof_len;
@@ -105,6 +108,8 @@

#define NOOF_TVECS (sizeof(tvecs) / sizeof(tvecs[0]))

+static inline void init_jiffieswrap_timer(void);
+
void init_timervecs (void)
{
int i;
@@ -117,6 +122,8 @@
}
for (i = 0; i < TVR_SIZE; i++)
INIT_LIST_HEAD(tv1.vec + i);
+
+ init_jiffieswrap_timer();
}

static unsigned long timer_jiffies;
@@ -699,6 +706,60 @@
if (TQ_ACTIVE(tq_timer))
mark_bh(TQUEUE_BH);
}
+
+
+#ifdef NEEDS_JIFFIES64
+
+u64 get_jiffies64(void)
+{
+ unsigned long j;
+ unsigned int f;
+
+ f = jiffies_msb_flips; /* avoid races */
+ rmb();
+ j = jiffies;
+
+ /* account for not yet detected flips */
+ f += (f ^ (j>>(BITS_PER_LONG-1))) & 1;
+ return ((u64) f << (BITS_PER_LONG-1)) | j;
+}
+
+/*
+ * Use a timer to periodically check for jiffies wraparounds.
+ * Instead of overflows we count flips of the highest bit so
+ * that we can easily check whether the latest flip is already
+ * accounted for.
+ * Not racy as invocations are several days apart in time and
+ * jiffies_flips is not modified elsewhere.
+ */
+
+static struct timer_list jiffieswrap_timer;
+#define CHECK_JIFFIESWRAP_INTERVAL (1ul << (BITS_PER_LONG-2))
+
+static void check_jiffieswrap(unsigned long data)
+{
+ mod_timer(&jiffieswrap_timer, jiffies + CHECK_JIFFIESWRAP_INTERVAL);
+
+ jiffies_msb_flips += 1 & (jiffies_msb_flips
+ ^ (jiffies>>(BITS_PER_LONG-1)));
+}
+
+static inline void init_jiffieswrap_timer(void)
+{
+ init_timer(&jiffieswrap_timer);
+ jiffieswrap_timer.expires = jiffies + CHECK_JIFFIESWRAP_INTERVAL;
+ jiffieswrap_timer.function = check_jiffieswrap;
+ add_timer(&jiffieswrap_timer);
+}
+
+#else
+
+static inline void init_jiffieswrap_timer(void)
+{
+}
+
+#endif /* NEEDS_JIFFIES64 */
+

#if !defined(__alpha__) && !defined(__ia64__)

--- linux-2.4.19-pre8/kernel/fork.c Sat May 4 19:31:42 2002
+++ linux-2.4.19-pre8-j64/kernel/fork.c Sat May 4 20:50:04 2002
@@ -661,7 +661,7 @@
}
#endif
p->lock_depth = -1; /* -1 = no lock */
- p->start_time = jiffies;
+ p->start_time = get_jiffies64();

INIT_LIST_HEAD(&p->local_pages);

--- linux-2.4.19-pre8/kernel/info.c Sat Apr 21 01:15:40 2001
+++ linux-2.4.19-pre8-j64/kernel/info.c Sat May 4 20:50:04 2002
@@ -12,15 +12,19 @@
#include <linux/smp_lock.h>

#include <asm/uaccess.h>
+#include <asm/div64.h>

asmlinkage long sys_sysinfo(struct sysinfo *info)
{
struct sysinfo val;
+ u64 uptime;

memset((char *)&val, 0, sizeof(struct sysinfo));

cli();
- val.uptime = jiffies / HZ;
+ uptime = get_jiffies64();
+ do_div(uptime, HZ);
+ val.uptime = (unsigned long) uptime;

val.loads[0] = avenrun[0] << (SI_LOAD_SHIFT - FSHIFT);
val.loads[1] = avenrun[1] << (SI_LOAD_SHIFT - FSHIFT);

--- linux-2.4.19-pre8/include/linux/kernel_stat.h Sun May 5 09:10:00 2002
+++ linux-2.4.19-pre8-j64/include/linux/kernel_stat.h Sun May 5 19:11:12 2002
@@ -16,9 +16,9 @@
#define DK_MAX_DISK 16

struct kernel_stat {
- unsigned int per_cpu_user[NR_CPUS],
- per_cpu_nice[NR_CPUS],
- per_cpu_system[NR_CPUS];
+ unsigned long per_cpu_user[NR_CPUS],
+ per_cpu_nice[NR_CPUS],
+ per_cpu_system[NR_CPUS];
unsigned int dk_drive[DK_MAX_MAJOR][DK_MAX_DISK];
unsigned int dk_drive_rio[DK_MAX_MAJOR][DK_MAX_DISK];
unsigned int dk_drive_wio[DK_MAX_MAJOR][DK_MAX_DISK];
--- linux-2.4.19-pre8/fs/proc/array.c Thu Oct 11 18:00:01 2001
+++ linux-2.4.19-pre8-j64/fs/proc/array.c Sat May 4 20:50:04 2002
@@ -343,7 +343,7 @@
ppid = task->pid ? task->p_opptr->pid : 0;
read_unlock(&tasklist_lock);
res = sprintf(buffer,"%d (%s) %c %d %d %d %d %d %lu %lu \
-%lu %lu %lu %lu %lu %ld %ld %ld %ld %ld %ld %lu %lu %ld %lu %lu %lu %lu %lu \
+%lu %lu %lu %lu %lu %ld %ld %ld %ld %ld %ld %llu %lu %ld %lu %lu %lu %lu %lu \
%lu %lu %lu %lu %lu %lu %lu %lu %d %d\n",
task->pid,
task->comm,
@@ -366,7 +366,7 @@
nice,
0UL /* removed */,
task->it_real_value,
- task->start_time,
+ (unsigned long long)(task->start_time),
vsize,
mm ? mm->rss : 0, /* you might want to shift this left 3 */
task->rlim[RLIMIT_RSS].rlim_cur,
--- linux-2.4.19-pre8/fs/proc/proc_misc.c Sat May 4 19:31:42 2002
+++ linux-2.4.19-pre8-j64/fs/proc/proc_misc.c Sun May 5 19:32:17 2002
@@ -40,6 +40,7 @@
#include <asm/uaccess.h>
#include <asm/pgtable.h>
#include <asm/io.h>
+#include <asm/div64.h>


#define LOAD_INT(x) ((x) >> FSHIFT)
@@ -67,6 +68,92 @@
extern int get_ds1286_status(char *);
#endif

+#if BITS_PER_LONG < 48
+static unsigned int uidle_msb_flips, sidle_msb_flips;
+static unsigned int per_cpu_user_flips[NR_CPUS],
+ per_cpu_nice_flips[NR_CPUS],
+ per_cpu_system_flips[NR_CPUS];
+
+static u64 get_64bits(unsigned long *val, unsigned int *flips)
+{
+ unsigned long v;
+ unsigned int f;
+
+ f = *flips; /* avoid races */
+ rmb();
+ v = *val;
+
+ /* account for not yet detected MSB flips */
+ f += (f ^ (v>>(BITS_PER_LONG-1))) & 1;
+ return ((u64) f << (BITS_PER_LONG-1)) | v;
+}
+
+#define get_uidle64() get_64bits(&(init_tasks[0]->times.tms_utime),\
+ &uidle_msb_flips)
+#define get_sidle64() get_64bits(&(init_tasks[0]->times.tms_stime),\
+ &sidle_msb_flips)
+#define get_user64(cpu) get_64bits(&(kstat.per_cpu_user[cpu]),\
+ &(per_cpu_user_flips[cpu]))
+#define get_nice64(cpu) get_64bits(&(kstat.per_cpu_nice[cpu]),\
+ &(per_cpu_nice_flips[cpu]))
+#define get_system64(cpu) get_64bits(&(kstat.per_cpu_system[cpu]),\
+ &(per_cpu_system_flips[cpu]))
+
+/*
+ * Use a timer to periodically check for overflows.
+ * Instead of overflows we count flips of the highest bit so
+ * that we can easily check whether the latest flip is already
+ * accounted for.
+ * Not racy as invocations are several days apart in time and
+ * *_flips is not modified elsewhere.
+ */
+
+static struct timer_list check_wraps_timer;
+#define CHECK_WRAPS_INTERVAL (1ul << (BITS_PER_LONG-2))
+
+static inline void check_one(unsigned long val, unsigned int *flips)
+{
+ *flips += 1 & (*flips ^ (val>>(BITS_PER_LONG-1)));
+}
+
+static void check_wraps(unsigned long data)
+{
+ int i;
+
+ mod_timer(&check_wraps_timer, jiffies + CHECK_WRAPS_INTERVAL);
+
+ check_one(init_tasks[0]->times.tms_utime, &uidle_msb_flips);
+ check_one(init_tasks[0]->times.tms_stime, &sidle_msb_flips);
+ for(i=0; i<NR_CPUS; i++) {
+ check_one(kstat.per_cpu_user[i], &(per_cpu_user_flips[i]));
+ check_one(kstat.per_cpu_nice[i], &(per_cpu_nice_flips[i]));
+ check_one(kstat.per_cpu_system[i], &(per_cpu_system_flips[i]));
+ }
+}
+
+static inline void init_check_wraps_timer(void)
+{
+ init_timer(&check_wraps_timer);
+ check_wraps_timer.expires = jiffies + CHECK_WRAPS_INTERVAL;
+ check_wraps_timer.function = check_wraps;
+ add_timer(&check_wraps_timer);
+}
+
+#else
+ /* Times won't overflow for 8716 years at HZ==1024 */
+
+#define get_uidle64() (init_tasks[0]->times.tms_utime)
+#define get_sidle64() (init_tasks[0]->times.tms_stime)
+#define get_user64(cpu) (kstat.per_cpu_user[cpu])
+#define get_nice64(cpu) (kstat.per_cpu_nice[cpu])
+#define get_system64(cpu) (kstat.per_cpu_system[cpu])
+
+static inline void init_check_wraps_timer(void)
+{
+}
+
+#endif /* BITS_PER_LONG < 48 */
+
static int proc_calc_metrics(char *page, char **start, off_t off,
int count, int *eof, int len)
{
@@ -98,34 +185,27 @@
static int uptime_read_proc(char *page, char **start, off_t off,
int count, int *eof, void *data)
{
- unsigned long uptime;
- unsigned long idle;
+ u64 uptime, idle;
+ unsigned long uptime_remainder, idle_remainder;
int len;

- uptime = jiffies;
- idle = init_tasks[0]->times.tms_utime + init_tasks[0]->times.tms_stime;
+ uptime = get_jiffies64();
+ uptime_remainder = (unsigned long) do_div(uptime, HZ);
+ idle = get_sidle64() + get_uidle64();
+ idle_remainder = (unsigned long) do_div(idle, HZ);

- /* The formula for the fraction parts really is ((t * 100) / HZ) % 100, but
- that would overflow about every five days at HZ == 100.
- Therefore the identity a = (a / b) * b + a % b is used so that it is
- calculated as (((t / HZ) * 100) + ((t % HZ) * 100) / HZ) % 100.
- The part in front of the '+' always evaluates as 0 (mod 100). All divisions
- in the above formulas are truncating. For HZ being a power of 10, the
- calculations simplify to the version in the #else part (if the printf
- format is adapted to the same number of digits as zeroes in HZ.
- */
#if HZ!=100
len = sprintf(page,"%lu.%02lu %lu.%02lu\n",
- uptime / HZ,
- (((uptime % HZ) * 100) / HZ) % 100,
- idle / HZ,
- (((idle % HZ) * 100) / HZ) % 100);
+ (unsigned long) uptime,
+ (uptime_remainder * 100) / HZ,
+ (unsigned long) idle,
+ (idle_remainder * 100) / HZ);
#else
len = sprintf(page,"%lu.%02lu %lu.%02lu\n",
- uptime / HZ,
- uptime % HZ,
- idle / HZ,
- idle % HZ);
+ (unsigned long) uptime,
+ uptime_remainder,
+ (unsigned long) idle,
+ idle_remainder);
#endif
return proc_calc_metrics(page, start, off, count, eof, len);
}
@@ -260,33 +340,39 @@
{
int i, len;
extern unsigned long total_forks;
- unsigned long jif = jiffies;
- unsigned int sum = 0, user = 0, nice = 0, system = 0;
+ unsigned int sum = 0;
+ u64 jif = get_jiffies64(), user = 0, nice = 0, system = 0;
int major, disk;

for (i = 0 ; i < smp_num_cpus; i++) {
int cpu = cpu_logical_map(i), j;

- user += kstat.per_cpu_user[cpu];
- nice += kstat.per_cpu_nice[cpu];
- system += kstat.per_cpu_system[cpu];
+ user += get_user64(cpu);
+ nice += get_nice64(cpu);
+ system += get_system64(cpu);
#if !defined(CONFIG_ARCH_S390)
for (j = 0 ; j < NR_IRQS ; j++)
sum += kstat.irqs[cpu][j];
#endif
}

- len = sprintf(page, "cpu %u %u %u %lu\n", user, nice, system,
- jif * smp_num_cpus - (user + nice + system));
- for (i = 0 ; i < smp_num_cpus; i++)
- len += sprintf(page + len, "cpu%d %u %u %u %lu\n",
+ len = sprintf(page, "cpu %llu %llu %llu %llu\n",
+ (unsigned long long) user,
+ (unsigned long long) nice,
+ (unsigned long long) system,
+ (unsigned long long) jif * smp_num_cpus
+ - user - nice - system);
+ for (i = 0 ; i < smp_num_cpus; i++) {
+ user = get_user64(cpu_logical_map(i));
+ nice = get_nice64(cpu_logical_map(i));
+ system = get_system64(cpu_logical_map(i));
+ len += sprintf(page + len, "cpu%d %llu %llu %llu %llu\n",
i,
- kstat.per_cpu_user[cpu_logical_map(i)],
- kstat.per_cpu_nice[cpu_logical_map(i)],
- kstat.per_cpu_system[cpu_logical_map(i)],
- jif - ( kstat.per_cpu_user[cpu_logical_map(i)] \
- + kstat.per_cpu_nice[cpu_logical_map(i)] \
- + kstat.per_cpu_system[cpu_logical_map(i)]));
+ (unsigned long long) user,
+ (unsigned long long) nice,
+ (unsigned long long) system,
+ (unsigned long long) jif -user -nice -system);
+ }
len += sprintf(page + len,
"page %u %u\n"
"swap %u %u\n"
@@ -322,12 +408,13 @@
}
}

+ do_div(jif, HZ);
len += sprintf(page + len,
"\nctxt %u\n"
"btime %lu\n"
"processes %lu\n",
kstat.context_swtch,
- xtime.tv_sec - jif / HZ,
+ xtime.tv_sec - (unsigned long) jif,
total_forks);

return proc_calc_metrics(page, start, off, count, eof, len);
@@ -580,4 +667,6 @@
slabinfo_read_proc, NULL);
if (entry)
entry->write_proc = slabinfo_write_proc;
+
+ init_check_wraps_timer();
}
--- linux-2.4.19-pre8/mm/oom_kill.c Sat May 4 19:32:07 2002
+++ linux-2.4.19-pre8-j64/mm/oom_kill.c Sat May 4 20:50:04 2002
@@ -69,11 +69,10 @@
/*
* CPU time is in seconds and run time is in minutes. There is no
* particular reason for this other than that it turned out to work
- * very well in practice. This is not safe against jiffie wraps
- * but we don't care _that_ much...
+ * very well in practice.
*/
cpu_time = (p->times.tms_utime + p->times.tms_stime) >> (SHIFT_HZ + 3);
- run_time = (jiffies - p->start_time) >> (SHIFT_HZ + 10);
+ run_time = (get_jiffies64() - p->start_time) >> (SHIFT_HZ + 10);

points /= int_sqrt(cpu_time);
points /= int_sqrt(int_sqrt(run_time));
--- linux-2.4.19-pre8/kernel/acct.c Sat Mar 30 19:13:16 2002
+++ linux-2.4.19-pre8-j64/kernel/acct.c Sat May 4 20:50:04 2002
@@ -56,6 +56,7 @@
#include <linux/tty.h>

#include <asm/uaccess.h>
+#include <asm/div64.h>

/*
* These constants control the amount of freespace that suspend and
@@ -227,20 +228,24 @@
* This routine has been adopted from the encode_comp_t() function in
* the kern_acct.c file of the FreeBSD operating system. The encoding
* is a 13-bit fraction with a 3-bit (base 8) exponent.
+ *
+ * Bumped up to encode 64 bit values. Unfortunately the result may
+ * overflow now.
*/

#define MANTSIZE 13 /* 13 bit mantissa. */
-#define EXPSIZE 3 /* Base 8 (3 bit) exponent. */
+#define EXPSIZE 3 /* 3 bit exponent. */
+#define EXPBASE 3 /* Base 8 (3 bit) exponent. */
#define MAXFRACT ((1 << MANTSIZE) - 1) /* Maximum fractional value. */

-static comp_t encode_comp_t(unsigned long value)
+static comp_t encode_comp_t(u64 value)
{
int exp, rnd;

exp = rnd = 0;
while (value > MAXFRACT) {
- rnd = value & (1 << (EXPSIZE - 1)); /* Round up? */
- value >>= EXPSIZE; /* Base 8 exponent == 3 bit shift. */
+ rnd = value & (1 << (EXPBASE - 1)); /* Round up? */
+ value >>= EXPBASE; /* Base 8 exponent == 3 bit shift. */
exp++;
}

@@ -248,16 +253,21 @@
* If we need to round up, do it (and handle overflow correctly).
*/
if (rnd && (++value > MAXFRACT)) {
- value >>= EXPSIZE;
+ value >>= EXPBASE;
exp++;
}

/*
* Clean it up and polish it off.
*/
- exp <<= MANTSIZE; /* Shift the exponent into place */
- exp += value; /* and add on the mantissa. */
- return exp;
+ if (exp >= (1 << EXPSIZE)) {
+ /* Overflow. Return largest representable number instead. */
+ return (1ul << (MANTSIZE + EXPSIZE)) - 1;
+ } else {
+ exp <<= MANTSIZE; /* Shift the exponent into place */
+ exp += value; /* and add on the mantissa. */
+ return exp;
+ }
}

/*
@@ -278,6 +288,7 @@
mm_segment_t fs;
unsigned long vsize;
unsigned long flim;
+ u64 elapsed;

/*
* First check to see if there is enough free_space to continue
@@ -295,8 +306,10 @@
strncpy(ac.ac_comm, current->comm, ACCT_COMM);
ac.ac_comm[ACCT_COMM - 1] = '\0';

- ac.ac_btime = CT_TO_SECS(current->start_time) + (xtime.tv_sec - (jiffies / HZ));
- ac.ac_etime = encode_comp_t(jiffies - current->start_time);
+ elapsed = get_jiffies64() - current->start_time;
+ ac.ac_etime = encode_comp_t(elapsed);
+ do_div(elapsed, HZ);
+ ac.ac_btime = xtime.tv_sec - elapsed;
ac.ac_utime = encode_comp_t(current->times.tms_utime);
ac.ac_stime = encode_comp_t(current->times.tms_stime);
ac.ac_uid = current->uid;
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2005-03-22 13:25    [W:0.046 / U:0.612 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site